Conventional technology pertaining to certain embodiments of the present invention is described in the following publications inter alia:
U.S. Pat. No. 5,274,545 to Allan describes a device and method for providing accurate time and/or frequency. A unit, such as an oscillator and/or clock provides output indicative of frequency and/or time. The device includes a processing section having a microprocessor that develops a model characterizing the performance of the device, including establishing predicted accuracy variations, and the model is then used to correct the unit output. An external reference is used to provide a reference input for updating the model, including updating of predicted variations of the unit, by comparison of the reference input with the unit output. The ability of the model to accurately predict the performance of the unit improves as additional updates are carried out, and this allows the interval between the updates to be lengthened and/or the overall accuracy of the device to be improved. The accuracy of the output is thus adaptively optimized in the presence of systematic and random variations.
U.S. Pat. No. 7,142,154 to Quilter describes a method and apparatus for providing accurately synchronized timing signals at mutually distant locations, employing a GPS or similar receiver at each location. These receivers are interconnected by a communications network, and exchange data over the network to agree with a common timing reference.
The disclosures of all publications and patent documents mentioned in the specification, and of the publications and patent documents cited therein directly or indirectly, are hereby incorporated by reference.